Antirust paper

ABSTRACT

PAPER BEARING A COATING COMPRISING AN ALKALINE EARTH METAL HYDROXIDE IN AN AMOUNT TO GIVE ANTIRUST PROPERTIES WHEN SUBJECTED TO CORROSIVE ENVIRONMENTS. THE ANTIRUST PAPER HAS A COATING OF AT LEAST 1 POUND OF CALCIUMN HYDROXIDE AND THE CALCIUM HYDROXIDE IS BOUND TO THE PAPER BY A WATER-DISPERSIBLE ADHESIVE WHICH IS NONGELLABLE IN THE PRESENCE OF CALCIUM IONS. THE COATING MAY CONTAIN AN ANTIGELLING AGENT TO PREVENT GELATION OF THE ADHESIVE IN THE PRESENCE OF CALCIUM IONS.

United States Patent 3,565,681 ANTIRUST PAPER Wally Z. Walters, Piedmont, and Michael F. Shillingburg, Keyser, W. Va., assignors to Westvaco Corporation, a corporation of Delaware No Drawing. Filed June 28, 1967, Ser. No. 649,460 Int. Cl. B32b 29/00; C09d /08 US. Cl. 117155 10 Claims ABSTRACT OF THE DISCLOSURE Paper bearing a coating comprising an alkaline earth metal hydroxide in an amount to give antirust properties when subjected to corrosive environments.

The antirust paper has a coating of at least 1 pound of calcium hydroxide and the calcium hydroxide is bound to the paper by a water-dispersible adhesive which is nongellable in the presence of calcium ions. The coating may contain an antigelling agent to prevent gelation of the adhesive in the presence of calcium ions.

BRIEF SUMMARY OF THE INVENTION This invention relates to antirust paper which is suitable for use as a label paper for metallic containers.

In the shipment and storage of canned foods, the atmospheric conditions encountered often promote corrosion of the metal can from the outside. As a reuslt of the can corroding, discoloration of the paper label surrounding the can occurs. Such damage to cans and labels has amounted to great proportions, especially for canned goods shipped by sea transport. Many attempts to prevent the corrosion of canned goods have been made, such as use of moisture barriers, desiccants, induction heating of cases of goods, use of cans made of enameled tin plate, and use of labels with low water absorptivity and low moisture vapor transmission, but none of these attempts have proven to be commercially successful.

Antirust or antitarnish papers, those papers which do not facilitate the oxidation of the metal being packaged, are known. Normally, such papers are made from rag or sulfite pulps, and the papers are often impregnated with chemicals such as metallic acetates. Other techniques include the addition of metallic compounds directly to the fiber furnish before the paper is formed or the impregnation of paper with chemicals which give off protective vapors and thereby inhibit corrosion. The latter technique involves the use of chemicals such as dicyclohexyl ammonium nitrate and dicyclohexyl ammonium fumarate. One difficulty encountered with many of the known antirust papers is that the antirust properties are not permanent and are lost upon exposure of the papers to the atmosphere.

We have discovered that an antitrust paper with substantially permanent antirust properties can be produced without the use of exotic chemicals or expensive pulps. Our invention is based on the discovery that paper hearing a coating of an alkaline earth metal hydroxide makes an excellent antirust paper. The coating is usually placed on the back side of the label paper, i.e., on the side of the label next to the can. It has been found that if the alkaline earth metal hydroxide is present on the paper in an amount equal to at least about 1 pound per 3300 square feet of paper, corrosion of iron is prevented or if any corrosion does occur, its products do not have any color and, therefore, do not stain the label. The novel antitrust papers of this invention do not lose their antirust properties upon exposure to sunlight, high or low humidities, or hot or cold temperatures.

The use of an alkaline earth metal hydroxide, such as calcium hydroxide or hydrated lime, as a coating pig- Patented Feb. 23, 1971 ice ment for paper is not a typical use of the material in the papermaking industry. However, we have found that such pigments can be the major component in a coating for an antirust paper. A suitable binder for the pigment is starch or a starchlatex mixture. The preferred coating for the antirust paper of this invention comprises an aqueous dispersion of hydrated lime, a starch-latex binder, a small proportion of an antigelling agent, such as sodium citrate or disodium phosphate, and a small amount of a plasticizer such as Avitone A, a mixture of parafiin waxes, or Nopco DC 1l0-A, a mixture of fatty acids. The starch-latex ratio is usually about 1 to 1 by weight but is flexible, and all starch may be replaced by equal parts of latex. Preferably, the latex employed has a high calcium ion tolerance and will not gel in the presence of lime. Suitable latices are butadiene-styrene latices such as Polyco 2415 (Borden Chemical Co.) and PCX 1705 (Union Carbide Corp.), and polyvinyl acetates, such as 1103A and 1103C (National Starch & Chemical Co.).

It has been found that novel antirust paper can be produced by coating paper with an aqueous dispersion of hydrated lime and starch, and substantially drying the coated paper to leave on the paper the dried residue of the aqueous dispersion. However, the dried, coated paper may have a tendency to dust, a condition which can be overcome by the use of a water-dispersible resin and/ or a plasticizer in the coating. It is to be understood, however, that the novel antitrust paper can be made without the use of any resin or plasticizer, as long as the hydrated lime is present on the paper in an amount of at least about 1 pound per 3300 square feet of paper and is substantially adhesively bonded thereto.

The amount of adhesive required will vary with respect to the particular adhesive employed and, therefore, it is difiicult to set forth minimum figures. The minimum amount of adhesive required is that amount sufficient to adequately bond the alkaline earth metal hydroxide pigment to the paper. For illustration purposes only, we have found that 12 parts total adhesive by weight per parts total pigment has proven satisfactory, and as much as 40 parts total adhesive have been in some instances.

As those skilled in the art will readily appreciate, the solids content of any of the novel antirust coating compositions can vary quite widely depending upon the particular process by which they are applied to the base paper and the coat weight desired. Coating compositions having solids contents of from about 17 to 55% have been used successfully in the present invention, with the preferred solids content running from about 30 to 40%. Also, coat weights may vary as high as desired, and coat weights up to about 8.2 pounds per ream have been employed. The pH of the coatings has varied from about 9 to 13.5, depending upon which of the alkaline earth metal hydroxides was used in the coatings.

The theory behind the excellent results with the antirust label paper produced according to the present invention is not fully understood. These results are not merely dependent upon the use of a calcium containing compound since it has been found that calcium carbonate and satin white do not provide the antirust properties obtained by using hydrated lime. Other alkaline earth metal hydroxides, such as barium hydroxide and magnesium hydroxide, have been employed successfully in the present invention as replacements for calcium hydroxide. Further, the coating is not a barrier coating. When the novel antirust paper is employed as label paper for cans, water can penetrate the label but rust is not formed. The good results are likewise not merely a result of pH since sodium hydroxide does not provide the desired antirust properties when used as a replacement for the alkaline earth metal hydroxides.

The invention is not limited to the use of a particular type of starch in the coating. Pearl, acid modified, cationic, oxidized, and ethylated starches have all performed well in the present invention. Protein adhesives, such as casein, may also be used as binder materials, as well as synthetic resins.

The coating can be applied to paper in any conventional manner, such as by tub sizing or surface size press or by use of a roll, blade, or air knife coater, The coated paper can be dried in any conventional manner and can be finished by the action of a machine calender or a supercalender.

DETAILED DESCRIPTION The invention will be better understood by reference EXAMPLES 89 Alkaline earth metal hydroxides other than calcium hydroxide can be employed in the practice of the present invention, and the readily available ones were tested. Aqueous coatings comprising barium hydroxide and binder, and magnesium hydroxide and binder, were prepared and applied separately by size press to the felt sides of traveling webs of paper. The data on the coatings and coated papers to the following illustrative examples. were as f ll s;

Pigment coat Percent Percent weight, binder on solids 1bs./ Pigment Binder pigment content 3,300 ft.

Example:

8 Barium hydroxide Ethylated starch 31. 5 2. 3 9 Magnesium hydroxide do 25 36. 0 3. 1

EXAMPLES l-7 Paper coating compositions comprising aqueous dispersions of calcium hydroxide or commercial hydrated lime and binder were prepared with the proportions of ingredients as indicated below. The aqueous coatings were separately applied at varying coat weights by a .0005 inch Bird film applicator to paper, made from sulfate pulp, having a basis weight of about 60 pounds per ream (500 sheets, 25 x 38 inches), and the coated paper was substantially dried. The paper had previously been coated on one side (wire side) with a standard paper coating composition comprising starch and clay, and the coatings below were applied to the side of the paper opposite to that previously coated (felt side). Various binders or adhesives were employed in the coatings to bind the pigment to the paper.

Some of the alkaline earth metal hydroxide in the coating can be replaced with coating clay. In this Example, 20 percent calcium hydroxide was replaced with hydrasperse clay. The coating formulation was:

Parts by wt. Hydrated lime 80 Hydrasperse clay 20 Ethylated starch 12 The starch was cooked in water at 190 F. for about 20 Pigment coat Percent Percent weight,

binder on solids lbs./

Pigment Binder pigment content 3,300 ft. Example:

1 Calcium hydroxide (0.1. grade) Casein 13 2. 2

2 do Enzyme eon rted starch- 13 45 2, 1

4 Commercial hydrated lime Casein 13 45 1. 8

0 Enzyme converted starch- 13 45 2. 2

Ethylated starch 20 35 3. 4

The coated papers, after drying, were conditioned at 72 F. and RH. and supercalendered six nips at 1000 pounds per lineal inch pressure loading. The papers were then tested for antirust properties.

The rust test performed is next described. Commercial tin cans (No. 303) were washed and oven dried, and then were spirally wrapped with chemically pure .009 inch iron wire, with inch spacing between strands. The wire ends were soldered at the can splice to insure tightness. Samples of the papers from Examples 1-7 were cut into strips 1 x 11 inches and placed tightly around the wire wrapped cans. The sides of the papers bearing the antirust coatings were placed against the wire in each instance. The cans were filled with ice water and were placed about one-half inch above a constant temperature bath held at 116 F., with the air above the water bath at F., for four hours. At the end of this time, much condensation had collected on the paper samples to the extent that the samples were thoroughly soaked with condensed water. The test strips were removed from the cans, air dried, and were evaluated for rust inhibiting characteristics.

The paper from Example 7, the control having the standard paper coating on the wire side but being untreated on the felt side, was greatly discolored from the rust which minutes in the presence of the lime and clay by use of direct steam. The resultant 1000 gallons of aqueous coating had a solids content of 30.5% and a Dudley viscosity of 48 at F.

The above coating was applied as an aqueous dispersion to the felt side of a web of paper of 49 pounds basis Weight by size press on a commercial-size paper machine. The coat weight was about 2.5 pounds per 3300 square feet of paper. After drying, the web of paper was coated on the opposite side with a standard coating formulation.

When tested, as described above, for its antirust properties, the antirust paper prevented rusting of the can and wire and no discoloration of the paper occurred. We have found that up to 50% of the alkaline earth metal hydroxide in the coating can be replaced by clay without any adverse elfect on the antirust properties of the coated paper, as long as the alkaline earth metal hydroxide is present in an amount of about one pound or more per 3300 square feet of the coated paper.

EXAMPLE 1 I As some dusting may occur between the size press and coater, the use of latex in the antirust coating may be beneficial under certain circumstances.

A coating, prepared as in Example 10, was modified to the extent that 8% starch and 8% butadiene-styrene latex, based on the weight of total pigment, were used as binder.

A coat weight of about 2 pounds per ream was applied to v a traveling web of 49 pounds basis weight, and the coated, dried web was completely free from dusting and exhibited excellent antirust properties when tested by the above procedure.

EXAMPLES 12-13 Example 12 Example 13 Hydrated lime, parts Sodium citrate, parts 4 4 Latex, butadiene-styrene, parts Ethylated starch, parts Plasticizer (Nopco DC 1l0-A) parts 5 5 Dispersing agent (Tamol 850), part 1 1 Percent solids content 40. 37. 8 Brookfield Viscosity at 100 F., c.p.s 2, 500 2, 200

In Examples 12 and 13, water, starch, and plasticizer were mixed and then treated with steam to cook the starch for about 20 minutes at about 190 F. The cooked starch was then added to a lime slip which had been formed by mixing the hydrated lime, soditun citrate, dispersing agent (polymeric sodium salt of an organic acid) and water, and the starch and the lime were mixed to form a smooth slurry. Finally, the latex was added to the starch-lime slurry to form the antirust coating compositions. The pH of the coating was about 12.5.

The aqueous coatings were applied in separate runs by a knurled roll coater to the felt sides of webs of paper having basis weights of about 45 pounds per ream. The amount of hydrated lime applied in Example 12 was about 3.2 pounds per 3300 square feet, and the amount applied in Example 13 was about 1.3 pounds. In each example the wire sides of the webs were coated with a conventional casein-clay coating composition after the antirust coatings were placed on the felt sides.

After substantially drying the coated webs on steam heated drier drums each exhibited excellent antirust properties when tested by the above procedure, and both webs were free from dusting. Control webs run in each instance, without the calcium hydroxide antirust coatings on the felt side, showed serious discoloration on both the felt and wire sides and were totally unsatisfactory as label papers.

From the above examples, it can be seen that novel antirust coatings and antirust papers have been set forth, as well as novel processes for producing the antirust compositions and papers. Laboratory and commercial trials have shown that effective antirust papers can be produced if the papers bear a coating comprising an alkaline earth metal hydroxide in an amount equivalent to about 1 pound per 3300 square feet of coated paper.

From the preferred examples, it is seen that the use of a small amount of an agent to prevent starch gelation, such as sodium citrate or disodium phosphate, is preferred when starch is used as the binder, but such agents are not a necessary ingredient in order to obtain antirust properties. Similarly, the use of a small amount of a plasticizer is preferred to avoid any dusting problems, but again such agents are not necessary for antirust properties; Further, any suitable water-dispersible binder may be employed to bind the alkaline earth metal hydroxide to the paper, such as starch alone, starch-latex combinations, casein and other proteins either alone or in conjunction with a synthetic resin, and synthetic resins alone. Obviously, all starch could be replaced by a resin, such as a butadiene-styrene latex or polyvinyl acetate, economics permitting.

Various changes may be made in the examples specifically set forth above without departing from the spirit of this invention or the scope of the appended claims.

We claim:

1. Antirust paper, suitable for use as label paper on metallic containers, consisting essentially of a paper sheet or paper web bearing on a surface thereof a coating comprising calcium hydroxide as pigment and a waterdispersible adhesive, non-gellable in the presence of calcium ions, selected from the group consisting of starch, protein, synthetic resins, and mixtures thereof, said calcium hydroxide pigment being present on the paper in an amount equal to at least about 1 pound per 3300 square feet of paper, said adhesive being present in an amount sufficient to bond the calcium hydroxide pigment to the paper, said coating being the substantially dried residue of an aqueous dispersion of the pigment and the adhesive.

2. Antirust paper according to claim 1 in which the adhesive is present in an amount equal to at least about 12 parts by weight per parts of pigment.

3. Antirust paper according to claim 2 in which the adhesive is starch.

4. Antirust paper according to claim 2 in which the adhesive is a mixture of starch and a synthetic resin.

5. Antirust paper according to claim 4 in which the coating further comprises an antigelling agent for the starch.

6. Antirust paper according to claim 4 in which the synthetic resin is a butadiene-styrene latex.

7. Antirust paper according to claim 4 in which the synthetic resin has a high calcium ion tolerance.

8. Antirust paper according to claim -4 in which the coating further comprises a plasticizer.

9. Antirust paper according to claim 4 in which the coating further comprises clay.

10. Antirust paper, suitable for use as label paper on metallic containers which are subject to corrosion in corrosive environments, consisting essentially of a base paper bearing on at least one surface a coating comprising calcium hydroxide, an adhesive comprising starch and a water-dispersible latex non-gellable in the presence of calcium hydroxide, and an antigelling agent for the starch, said calcium hydroxide being present on the paper in an amount equal to at least about 1 pound per 3300 square feet of coated paper, said adhesive being present in an amount equal to about 12 to 40 parts by weight per 100 parts calcium hydroxide in the coating and bonding the calcium hydroxide to the paper, said coating being the substantially dried residue of an aqueous dispersion of the calcium hydroxide, adhesive, and antigelling agent.

References Cited UNITED STATES PATENTS 1,598,104 8/1926 Rafsky 162-181 1,934,639 11/1933 Rafton 117-152X 2,417,064 3/1947 Cox 21-25 2,537,114 1/1951 Young et al. 1l7-155 2,639,989 5/1953 Conover 117-152X 2,709,653 5/1955 Marshall et al. 212.5X 2,711,377 6/1955 Riddell 117-169X (Other references on following page) UNITED STATES PATENTS i Ross .et a1. 21-25 Hanson 117152X Gallino 117155X Robinson et a1. 117155X Randall 117155X Bicknell 117155X Peterson et a1 117155X Smith 117155X 8 OTHER REFERENCES A.P.C. application of G. H. Vulliet-Durand, Ser. No.

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